1. Field of the Invention
The present invention relates generally to read head portions of magnetic heads for hard disk drives and more particularly to current perpendicular to plane (CPP) tunnel junction read sensors for magnetic heads.
2. Description of the Prior Art
A computer disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head reads from or writes data to concentric data tracks defined on surface of the disks. The heads are fabricated in structures called “sliders” and the slider flies above the surface of the disk on a thin cushion of air, where the surface of the slider which faces the disks is called an Air Bearing Surface (ABS).
Some recent read sensor structures use a tunnel junction sensor, also known as a “tunnel valve” for reading the magnetic field signals from the rotating magnetic data storage disk. The tunnel junction sensor typically includes a nonmagnetic tunnel barrier layer sandwiched between a pinned magnetic layer and a free magnetic layer. The pinned layer in turn is fabricated on an antiferromagnetic (AFM) pinning layer which fixes the magnetic moment of the pinned layer at an angle of 90 degrees to the air bearing surface (ABS). The magnetic moment of the free layer is free to rotate from a quiescent or zero bias point position in response to magnetic field signals from magnetic data bits written on the rotating magnetic disk. Hard bias elements are typically disposed on either side of the free magnetic layer to provide the necessary magnetization bias for the free magnetic layer. The tunnel junction sensor layers are typically disposed between first and second magnetic shield layers, where these first and second shield layers also serve as first and second electrical lead layers for conducting a sensor current through the device. The tunnel junction sensor is thus configured to conduct sensor current perpendicular to the planes (CPP) of the film layers of the sensor, as opposed to previously developed sensors where the sensor current is directed in the planes (CIP) or parallel to film layers of the sensor. The CPP configuration is attracting more attention recently, as it apparently can be made to be more sensitive than the CIP configuration, and thus is more useful in higher data density tracks and disks.
Improved hard disk drives are manufactured with an ever increasing areal data storage density, which requires narrower and more closely spaced data tracks on the hard disk. As a result, size of the read sensors must be reduced, and as the size of the sensors is reduced the stabilization of the free magnetic layer by the hard bias elements is becoming a problem. Additionally, the stabilization of the hard bias elements has also become a problem where the sensors are reduced in size.